Welcome to the ins and outs of using Ventrilo on your Macintosh. Please read through this post before creating your own as your question will have been most likely answered here.

1) Can I use Ventrilo on Macintosh?

Yes, Ventrilo is written for and supported on the Macintosh OS, and it works on 10.5 (Leopard) and 10.6 (Snow Leopard)

2) Codec's and You; a brief explanation

Voice communication over the internet is done using codec's (coder/decoder). You computer samples your voice, codes it, sends to to the listener, whose computer decodes it so they can hear you. There are many codecs but the ones in question here are GSM and Speex, and Ventrilo supports both.

They are both fairly equal in quality, however GSM is a proprietary codec that developers must pay a fee to use. Speex on the other hand is open-source and available to anyone who wants to use it.

Years ago, Apple opted to not include the GSM codec in their operating system, and because they didn't, GSM is not available on the Mac. However, Speex is so in order for your Mac to work with Vent, it needs to talk to a server that is set up to use the Speex codec. (it sounds limiting, but isn't read on)

The folks at Flagship, who make Ventrilo made a brilliant programming move by making the Ventrilo client auto-adjust depending on what the server settings are; so if you have a server that is set to GSM, and it is then changed to Speex, all of the clients will change themselves automatically, and the user never knows it happened.

So, to get your Macintosh Client working, the server you connect to will need to be set to Speex. If it isn't set to that already, contact whoever administers the Ventrilo server and have them make the change - it will literally take them about 30 seconds.

On a personal note, we have seen dozens of guilds/vent users change over to Speex and the feedback we get is that not only is the sound quality better, it also better stability - your mileage may vary.

3) What settings should the Vent Server have so I can connect with my Mac?

Your server should be set to Speex Codec, which it may be already, if not, contact your Vent Administrator

There are dozens of different settings for Speex codecs, and a lot of getting the best one for your server is trial and error. However, Speex 16 KHz, 16 bit, 10 Qlty is a good starting point - if vent users experience lag or dropouts lower the setting to 5 Qlty, and try it. Then lower it to 8 bit etc etc

4) Macintosh Configuration:

You tell your Mac how you want to listen to audio (iTunes, Vent, Game sounds etc) and how it should listen to you (Vent) via the Sound System Preference. There are three tabs in Sound, Sound Effects, Output and Input.
Output: tells your Mac where you want sound to go, you can select Speakers, Headphone Jack or if you have a USB Headset, to the name of the headset or possibly Unknown USB Device.
Input: tells your Mac where to get it's sound from; build in Mic, Line In or in the case of a USB Headset, either the name of the headset or Unknown USB Device

Ventrilo has it's own subset of where to get sound from and direct sound to. So for example, say you wanted iTunes and WoW to play through your Mac Speakers but you want to listen to Vent through your headset and want to speak through your headsets Mic.

a) Set the Sound System preference output to Computer Speakers.
b) Set the Input to Unknown USB Device (or the name of your headset)

then in Vent Setup

a) Set Sound Output to Unknown USB Device (or the name of your headset)
b) Set Input to Unknown USB Devier (or the name of your headset)

(note there are dozens of different way to configure audio so play with it)

5) Can't hear anything

To start with, see #2 above and then see #4 above.
#1 fix is to look at the bottom on the main Vent window and make sure Mute Sound is NOT checked.

6) Can't connect to server

This is very common when the server information is not correct. All vent servers have an address (either a set of numbers or words like www.someventriloserver.com) and a port number. That information must be 100% accurate or you won't be able to connect.
There is also the slight chance that the router or firewall you are using is blocking Ventrilo, so a restart of the router and/or checking to make sure vent (port #3784 tcp & UDP) is not blocked.

You can also go to http://ventrilo.com/status.php and enter the hostname and port number of the vent server you are trying to connect to make sure it is working properly.

7) Robotic Static Sound

This is a known issue, and is probably related to the Macintosh OS. Also possible that an updated version of Vent will fix it (hint hint Flagship). Please see this thread on the Apple Discussions forum

8) PTT (Push to talk) key doesn't work, or only works when the Vent window is active.

Nine times out of 10, this is because the Key you selected to be your Push To Talk key is already used by another application. If you are playing WoW, check your Key Bindings to see if they key is already used, and either change that Key Binding or change your PTT key
or
Exit Vent
Goto - System Preferences -> Universal Access -> Enable access for assistive devices (turn it on)
Then restart Ventrilo
or
Check Ventrilo->Setup and make sure the Use Push-To-Talk Hotkey checkbox is checked and you have a hot key set up.

9) I keep changing the Codec in my Vent Settings and it changes back.

That's actually not a 'setting'. It is only a temporary change to test your sound quality & mic. Vent get's it's codec setting from the Vent server and you cannot change it on the client end. See 2) above.

10) Right Click on a MacBook or MacBook Pro

You can right click by either Command-Clicking (or tapping), or go to System Preferences -> Trackpad and set up a gesture for right clicking, like setting it to two-finger tapping to be a right click.

11) Vent starts up, but no Vent Window

(from Prog-Rocker)
It's possible the vent window location is located off screen.

goto {login name}/library/preferences/ventrilo folder/edit the ventrilo2.ini/remove the line "MainLocSize=#,#,#,#"/save the file and start vent

12) Everything works, I can hear others, and when I press PTT, my icon lights up but no-one can hear me.

Three possibilities
a) You headset/mic may have a manual MUTE button on it. Make sure it is not muted ;-)
b) At the bottom of the main Vent window, makes sure Mute Microphone/Binds is NOT checked
c) You may need to boost your Mic input. There is a setting in System Preferences->Sound as well as in Ventrilo->Setup Amplifiers section Output slider to max.